1. Field of the Invention
The present invention relates to a dielectric ceramic which is advantageously used in a laminated ceramic electronic element such as a laminated ceramic capacitor having an internal conductor formed of a base metal such as nickel or nickel alloy, and to a method for producing the dielectric ceramic. The present invention also relates to a laminated ceramic electronic element which is formed of the dielectric ceramic and to a method for producing the same.
2. Description of the Related Art
Miniaturization and cost reduction of laminated ceramic electronic elements is in progress. For example, the ceramic layer has been thinned and a base metal has been employed as an internal conductor in such a ceramic electronic element. In the case of a laminated ceramic capacitor, which is one type of laminated ceramic electronic element, the dielectric ceramic layer has been formed as thin as about 3 .mu.m and a base metal such as Cu or Ni has been employed as a material for producing an internal conductor, i.e., an internal electrode.
However, when the ceramic layer becomes thin, the strength of an electric field applied to the layer increases and causes a problem in that the ceramic layer dielectric exhibits a great change in dielectric constant induced by the electric field. Decrease of the size of ceramic grains in the thickness direction of the ceramic layer also causes a problem in reliability.
In order to cope with such situations, Japanese Patent Application Laid-Open (kokai) Nos. 9-241074, 9-241075, etc. have proposed ceramic materials which enable enhanced reliability by increasing the size of ceramic grains in the thickness direction of the dielectric ceramic layer. Thus, controlling the grain size of ceramic grains allows a reduction in change of dielectric constant induced by an electric field or temperature.
However, in the above-described conventional art, although reliability is maintained when the thickness of a dielectric ceramic layer is about 1 .mu.m or less, variation in temperature-dielectric constant characteristics increases to thereby make it difficult to obtain products having stable temperature-dielectric constant characteristics with high reproducibility. In order to ensure stable temperature-dielectric constant characteristics, field intensity must be lowered and the rated voltage of the resultant laminated ceramic electronic elements has to be lowered. Therefore, realization of a thin layer having a thickness as thin as about 1 .mu.m or less is difficult or impossible so long as the above-described conventional art is employed to solve the problem.